In the field of liquid compositions for treating the surface of tin-plated DI can, one example of related art is the invention disclosed in (1) Japanese Patent Application Laid Open [Kokai or Unexamined] Number 01-100,281 [100,281/89] by the assignee of the present applicants. This particular invention comprises a film-forming liquid composition for the treatment of metal surfaces in which the liquid composition has a pH of 2 to 6 and contains 1 to 50 g/L phosphate ion, 0.2 to 20.0 g/L oxyacid ion, 0.01 to 5.0 g/L tin ion, and 0.01 to 5.0 g/L condensed phosphate ion. Treatment with this liquid composition lays down a strongly corrosion-resistant phosphate film on the surface of tin-plated DI can.
In addition, the invention disclosed in (2) Japanese Patent Application Laid Open Number 01-172,406 [172,406/89] is an example of a treatment method intended to develop corrosion resistance and adherence through the use of water soluble resin. This invention comprises a method for treating metal surfaces with a solution which contains a derivative of a suitable polyhydric phenol compound.
Furthermore, during the metal can manufacturing process, the high friction coefficient of the exterior can surface causes the can surface to have a poor slideability during conveyor transport of the can, which often causes the can to tumble over sideways and thus impairs the transport operation. Can transportability is a particular issue with respect to transport to a printer. It is therefore necessary in the can-manufacturing industry to reduce the static friction coefficient of the exterior can surface without compromising the adherence of any paint or lacquer to be coated on the can. The invention disclosed in (3) Japanese Patent Application Laid Open Number 64-85292 [85,292/89] is an example of a method for improving the slideability. This invention concerns an agent for treating the surfaces of metal cans. This particular agent contains water soluble organic material selected from phosphate esters, alcohols, monovalent and polyvalent fatty acids, fatty acid derivatives, and mixtures of the preceding.
It has already been discovered that a film with an excellent corrosion resistance, excellent paint adherence, and improved slideability can be formed on the can surface through the use of a surface treatment liquid composition which characteristically comprises an aqueous solution with a pH of 2.0 to 6.5 which contains 1 to 30 g/L of phosphate ions, 0.1 to 5 g/L of condensed phosphate ions, and 0.1 to 20 g/L (as solids) of a water soluble resin (poly{vinyl-phenol-amino} compound). This has been the subject of an antecedent patent application (Japanese Patent Application Number 02-160,443 [160,443/90]).